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Discussion in 'Beginner Electronics' started by Henry, Dec 25, 2005.

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  1. Henry

    Henry Guest

    I am tinkering with some 25 year old TTL logic chips and I need to make a
    de-bounce circuit that will stay on for the duration of a the push-button. I
    have several ways already to debounce the button close, but they are
    one-shot pulses that have thein own duration. I need both the close and open
    of the push button to be debounced and it to keep the duration of the button
    push. I have seen schmitt trigger circuits (that I have tried to build but
    dont seem to work (have to triple check the wiring)), and other RC
    variations. What kind of easily accessible parts (like from Radio Shack)
    should I be looking for. It all has to run on 4-AA batteries. Looked an some
    op-amp parts at RS but they seem to all require 18v, or more, supply.

    BTW, the debouncing solution needs to be acurate to within about 1

  2. Dan Hollands

    Dan Hollands Guest

    The easiest way is to use a pushbutton with Form C contact (single pole,
    double throw) connected to 2 cross connected NOR gates so that when the
    moving contact hits one pole connected to one NOR gate the cross connection
    latches in one state and when the moving contact hits the other pose
    connected to the other NOR gate the cross connection latches in the other
    state. Thus you get a latch circuit the follows the pushbutton with no

    If you don't know how to implement this let me I can give you more details


    Dan Hollands
    1120 S Creek Dr
    Webster NY 14580
  3. Henry

    Henry Guest

    Thanks, but I have no control over the push button. Its a camera shutter.
    Might be mechanical, might be electronic. Either way it acts like a simple
    push button closing a circuit. The mechanical ones, of course have noise.

    I have an old camera that I want to try some specialy effects photography
    with. I also have a view camera that has a focal plane leaf shutter (built
    into the lens) that, in theory, should sync with a flash through its range
    of shutter speeds (up to 1/250 of a second.)

    Anyway, thanks. I will keep looking.

  4. Dan Hollands

    Dan Hollands Guest


    Without some knowledge of the type and electrical charactoristis of the
    button it is hard to design a debounce circuit. Even with a mechanical
    switch are sure that need one - what is the button going to do

    Dan Hollands
    1120 S Creek Dr
    Webster NY 14580
  5. Henry

    Henry Guest

    Yes, I have read how difficult of a problem that it is. And what makes it
    worse is that I wanted to make it a general circuit good for mony, if not
    most, camera shutters whether they be mechanical or digital. One of the
    things is that I wanted to make a timer to measure how long a shutter is
    open (old mechanical camera shutters can vary (as much as 20%) from the
    indicated shutter speed. I have an idea for a solution, but is seems odd.

  6. Henry

    Henry Guest

    Thanks for the link and I have already been to that site. Great site and I
    am using it as one of my references.

    Problem is that I dont have any 74 series with schmitt triggers. I looked
    thourgh my box of old TTL chips. I have nand gates, counters, flipflops, 555
    timers, (plus transistors, resistors, capacitors, etc) but nothing with a
    schmitt trigger built in. Being out in a rural area and financially drained
    (from caregiving for my mother in her last years) I can not justify $25
    minimum ordering with S&H for a $0.49 chip. Radio Shack does not carry
    these, and my attempts to build my own from transistors in my
    box-o-ole-lectronics seems to have failed. Lacking a scope I cant really
    tell if what I assemble is working. So I am continuing by trial and error.
    All I know is that with what I have built so far I am getting multiple
    triggers from the old camera shutter that I have. That is my noisy switch
    that I am using.

  7. Henry

    Henry Guest

    Henry, please bottom post, since it makes it much easier to follow
    Thanks, I will try to keep that is mind. Im on several different forums
    (photography, sci-fi, etc.) and different ones have different preferences,
    if any. Ussually I follow with what the last person used, or I try to.

    Thanks everyone for all the help and suggestions. I will be giving several
    suggested circuits a try soon. Assuming that I can build them correctly, and
    have the parts.

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